Antioxidative Fish Oil

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Eur. J. Lipid Sci. Technol. 2012, 114, 434445

Research Article The antioxidative effect of lipophilized rutin and dihydrocaffeic acid in sh oil enriched milkAnn-Dorit Moltke Srensen1, Lone Kirsten Petersen1*, Sara de Diego2**, Nina Skall Nielsen1, Bena-Marie Lue3***, Zhiyong Yang3, Xubing Xu3 and Charlotte Jacobsen11

Division of Industrial Food Research, National Food Institute, Technical University of Denmark, Lyngby, Denmark 2 Department of Biotechnology and Food Science, University of Burgos, Burgos, Spain 3 Department of Engineering, Aarhus University, Arhus, Denmark

The antioxidative effect of phenolipids was evaluated in sh oil enriched milk emulsions as a model for a complex food system. Two different phenolipids modied from dihydrocaffeic acid (with C8 or C18:1) and rutin (with C12 or C16) were evaluated. Both dihydrocaffeate esters and rutin laurate showed signicantly better antioxidant properties in milk emulsion compared with the original phenolics. However, rutin palmitate only performed slightly better as antioxidant than rutin. The results with rutin indicated that a cut-off effect exists in relation to the alkyl chain length with respect to optimal antioxidant activity in milk emulsions. Thus, the optimal alkyl chain length is at least below 16 carbon atoms, and maybe even less for rutin esters. For dihydrocaffeate esters it was not possible to conclude on a cut-off effect in relation to alkyl chain length and antioxidative effect due to the almost similar antioxidant effect of the two phenolipids. However, there was a tendency towards octyl dihydrocaffeate being slightly more efcient than oleyl dihydrocaffeate. Practical application: The nding that phenolipids are better antioxidants in milk emulsions than the original phenolic acid provides new knowledge that can be used to develop new antioxidant strategies to protect foods against lipid oxidation. However, the results indicate that both optimization of alkyl chain length for each type of phenolic, and optimization for each type of emulsion will be necessary in order to get the best oxidative stability of an emulsion with these phenolipids. Use of efcient antioxidants may lower the amount of antioxidant needed to protect against lipid oxidation and may in addition decrease the costs.Keywords: Caffeic acid / o/w Emulsion / Polar paradox / Rutin

Received: October 10, 2011 / Revised: January 9, 2012 / Accepted: February 24, 2012 DOI: 10.1002/ejlt.201100354

1 IntroductionThe health benecial effects of n-3 long chain PUFA (LC PUFAs) such as, e.g. reduced risk of cardiovascular diseases are well documented. During the last decade substantial

Correspondence: Dr. Ann-Dorit Moltke Srensen, Division of Industrial Food Research, National Food Institute, Technical University of Denmark, Sltofts Plads, Building 221, DK-2800 Kgs. Lyngby, Denmark E-mail: adms@food.dtu.dk Fax: 45 4588 4774 Abbreviations: ATD, automatic thermal desorber; BHT, butylated hydroxytoluene; DHCA, dihydrocaffeic acid; DHCA C18:1, oleyl dihydrocaffeate; DHCA C8, octyl dihydrocaffeate; EPA, eicosapentaenoic acid; LC, long chain; PV, peroxide value; Rutin C12, rutin laurate; Rutin C16, rutin palmitate

efforts have been put into enriching foods with the healthy n-3 LC PUFAs as reviewed by Jacobsen et al. [1] These efforts have been carried out in order to increase the populations intake of especially eicosapentaenoic acid (EPA) and DHA [2, 3]. Despite the increasing number of n-3 PUFA enriched foods on the market, consumer acceptance and shelf-life of such products are still limited by the higher oxidative susceptibility of unsaturated lipids, which will lead to an unpleasant shy off-avour [47]. To retard lipid oxidation, a range of commercial synthetic antioxidants with free radical scavenging activity and metal chelating properties are*Current address: CP Kelco ApS, Ved banen 16, DK-4623 Lille Skensved, Denmark **Current address: Grupo Siro, Paseo Pintor Rosales 40, Madrid, Spain ***Current address: Novozymes A/S, Krogshoejvej 36, DK-2880 Bagsvaerd, Denmark

2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Eur. J. Lipid Sci. Technol. 2012, 114, 434445

Antioxidant efficacy of lipophilized phenolics

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available, e.g. calcium disodium ethylenediaminetetraacetate (EDTA), butylhydroxytoluene (BHT) and propyl gallate. However, there is a trend in consumer preference for natural ingredients such as phenolic compounds rather than synthetic compounds. The major part of natural antioxidants from plants, are phenolic compounds, e.g. caffeic acid. Most food products are emulsions, and in these systems lipid oxidation is suggested to be initiated at the interface between the oil phase and the aqueous phase or air, and continued in the oil phase. In emulsions, antioxidants may mainly partition into three different phases: the aqueous phase, the oil phase and the interface between oil and water. Partitioning of antioxidants into the different phases is inuenced by their polarity and interactions with other components present in the emulsion, e.g. emulsier [8, 9]. Generally, phenolics are hydrophilic compounds and they will most likely be located in the aqueous phase. Furthermore, the polarity of antioxidants in bulk oil and emulsions has been considered to be decisive for their efciency. This phenomenon is known as the polar paradox and states that hydrophilic antioxidants are more efcient in bulk oils than lipophilic antioxidants. In contrast, lipophilic antioxidants generally function better than hydrophilic antioxidants in emulsions [10]. However, recent studies have reported results that contradict the polar paradox hypothesis [1114]. This suggests that other factors might be equally important, and more research is urgently required to improve our understanding about the relationship between the molecular structure of the antioxidants and their efcacy in different real food systems. Recently, several studies have reported the possibility of changing the polarity of phenolics by lipophilization with fatty acids of different chain length in order to improve their antioxidative effect in emulsied media. The current work in this area has been summarized by Shahidi and Zhong [15]. Laguerre et al. [11, 16] have recently reported on the antioxidative effect of lipohilized chlorogenic and rosmarinic acids. For chlorogenic acid the antioxidant capacity increased as the alkyl chain length was increased from 1 to 12 carbon atoms, whereas further increase of the chain length resulted in a drastic decrease in the antioxidant capacity. On the basis of these results the authors suggested a so-called cut-off effect related to the length of the lipid chain attached to chlorogenic acid, which they explained as follows: When, the hydrophobicity of the lipophilized compound increases to above a certain level, the lipophilized compound is suggested to form micelles in the aqueous phase. Thereby, they will not be available as antioxidants at the interface and in turn their efcacy will be reduced [11]. For rosmarinate esters, the octyl rosmarinate improved the antioxidative effect eight times compared to rosmarinic acid. Thus, the results lead to the conclusion that lipophilization with medium chain fatty acids is a promising way to increase the antioxidant activity [16]. However, the results obtained with chlorogenate and rosmarinate esters have also led to the suggestion that the exact 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

location of antioxidants in the discontinuous phase, interfacial layer or oil droplets, is important for the activity of the antioxidants [11, 16]. In addition, a study on lipophilized dihydrocaffeic acids and their antioxidative effect in o/w emulsions reported by Srensen et al. [17] suggested that lipophilized dihydrocaffeic acid tended to follow the newly suggested cut-off effect in relation to the alkyl chain length attached although only two chain lengths were evaluated. In contrast, lipophilized rutin added to o/w emulsions did not show a cut-off effect, since the esters, rutin laurate and rutin palmitate, were consistently less effective compared with the rutin [13]. However, only two chain lengths (C12 and C16) were evaluated along with rutin, hence alkyl chain shorter than C12 lipophilized on rutin may indicate a cut-off effect. From these studies it may be concluded that the cut-off effect is specic for the individual lipophilized phenolic compounds, i.e. the optimal chain length may vary between different phenolics. Recent research on lipophilized phenolic compounds has mostly paid attention to their production, in vitro antioxidant activity and their effect in simplied model systems, whereas studies on their effect in real food systems are lacking. In more complex systems such as real food the antioxidant behaviour might be inuenced by interaction with other components present in the emulsions, e.g. emulsier and iron [15, 18]. However, on the basis of studies in simple o/w emulsions we hypothesize that lipophilization of phenolics will increase their antioxidant efcacy in emulsied food enriched with n-3 PUFAs. Moreover, we hypothesize that the alkyl chain length will affect the antioxidative effect of these lipophilized phenolic compounds as was observed in a recent study with simple o/w emulsions [17], and that the effect of the alkyl chain length may be different from that observed in simple model systems due to the presence of other potentially interacting compounds. Therefore, the aim was to evaluate the antioxidative effect of dihydrocaffeic acid lipophilized with either octyl or oleyl alcohol and rutin lipophilized with lauric acid or palmitic acid in sh oil enriched milk. Fish oil enriched milk was chosen as previous studies have shown that it is highly susceptible to lipid oxidation [1]. Moreover, it is a complex food